1. Field of the Invention
The present invention relates to the field of nanomaterials such as carbon nanotubes and further to the field of thermal switches.
2. Related Art
Presented below is background information on certain aspects of the present invention as they may relate to technical features referred to in the detailed description, but not necessarily described in detail. The discussion below should not be construed as an admission as to the relevance of the information to the claimed invention or the prior art effect of the material described.
Unlike electrical resistivity, which can vary by more than 1012 from insulators to metals, thermal conductivity varies by less than 104 from the best thermal conductors to the best thermal insulators. In addition, unlike typical field-effect transistors, which can change on-off resistances by more than 106, no devices have been shown to exhibit tunable thermal conductance. This lack of variability and tunability of phonon transport in materials is the main obstacle for heat management and further processing of phonons as information carriers. Thus, there is a need in the art for devices that provide variable control of thermal conductance.
Specific Patents and Publications
Terraneo et al., “Controlling the energy flow in nonlinear lattices: A model for a thermal rectifier”, Physics Review Letters, 88, 094302 (2002), describes a model of a thermal diode based on resonance. In the model, a nonlinear material with a resonant frequency that depends strongly on temperature was sandwiched between two nearly linear segments, the frequencies of which exhibit little variation with temperature. The model suggests that the frequencies of materials match one another when a temperature drop is introduced in one direction and mismatch one another when the temperature drop is in the other direction, thus allowing heat to flow through the sandwich in one direction but not the other.
Li et al., “Thermal diode: Rectification of heat flux,” Physics Review Letters, 93, 184301 (2004), expands on Terraneo's model by using segments made up of a chain of particles subject to a sinusoidal potential. This model also reduced the number of segments from three to two. The model increased the rectification effect by up to three orders of magnitude.
Chang et al., “Solid-state thermal rectifier,” Science, 314, 1121 (2006) describes a nanoscale solid-state thermal rectifier. The rectifier uses high-thermal-conductivity carbon or boron nitride nanotubes mass-loaded externally and inhomogeneously with heavy molecules.
Li et al., “Negative differential thermal resistance,” Appl. Phys. Lett., 88, 143501 (2006) describes a model of a thermal transistor to control heat flow. The thermal transistor comprises a three-terminal device with the important feature that the current through the two terminals can be controlled by small changes in the temperature or in the current through the third terminal. This control feature allows switching of the device between “off” (insulating) and “on” (conducting) states or to amplify a small current
U.S. Pat. No. 6,034,408, “Solid state thermal switch,” issued to Goshal, describes a solid-state thermal switch providing thermal conductivity in the on state and enhanced thermal isolation in the off state. The device includes a cracked, thin semiconducting layer that has a drain and a source etched into it.
Cumings et al. US 2002/0070426 A1 discloses a method for forming a telescoped multiwall carbon nanotube (“MWCNT”). Such a telescoped multiwall nanotube is shown in this publication to act as a linear bearing in an electromechanical system. That is, the walls of a multiwalled carbon nanotube are concentrically separated and are shown to telescope axially inwardly and outwardly. In Science 289:602-604 (28 Jul. 2000), a scientific publication related to the 2002/0070426 A1 patent publication, Cumings and Zettl describe a low friction nanoscale linear bearing, which operates in a reciprocal (i.e., movable) manner.
Barreiro et al., “Subnanometer Motion of Cargoes Driven by Thermal Gradients Along Carbon Nanotubes,” Science 320 775-778 (May 9, 2008) describes an artificial nanofabricated motor in which one short carbon nanotube moves relative to another coaxial nanotube. A cargo is attached to an ablated outer wall.